Sydnocarb (i.e., 3-(β-phenylisopropyl)-N-phenylcarbamoylsydnonimine), also known as mesocarb, is a psychomotor stimulant. In Russia, sydnocarb has been used for over 30 years to treat a variety of neuropsychiatric comorbidities such as asthenia, apathy, and adynamia (Anokhina et al., Zh Nevropatol Psikhiatr Im S S Korsakova, 1974, 74, 594-602; Vinar et al., Neuropsychopharmacology, 1991, 5, 201-217; and Cody, J. Occup. Environ. Med., 2002, 44, 435-450). Although mostly anecdotal, evidence may suggest that sydnocarb increases endurance during heavy physical activity and resistance to environmental stressors such as hypothermia, low gravity, and oxygen deprivation. Sydnocarb may also have beneficial effects in treating alcohol abuse, attention deficit hyperactivity disorder (ADHD), and cognitive impairment (Rudenko et al., Agressologie, 1979, 20, 265-270; Vinar et al., supra; Cody, supra).
Although sydnocarb-induced facilitation of dopamine (DA)-mediated transmission has been well established in microdialysis studies, the exact nature of this action (i.e., DA release versus DA transporter (DAT) inhibition) is not clear (Gainetdinov et al., Eur. J. Pharmacol., 1997, 340, 53-58; Afanas'ev et al., Pharmacol. Biochem. Behav., 2001, 69, 653-658; Anderzhanova et al., Eur. J. Pharmacol. 2001, 428, 87-95). More recently, it has been demonstrated that sydnocarb has DAT activity and lacks the rebound hypersomnolence, characteristic of compounds that cause dopamine release (Gruner et al., J. Pharmacol. Exp. Therap., 2011, 337, 380-390). It has been reported that sydnocarb attenuates noradrenaline reuptake based on experiments in rat synaptosomes (Erdö et al., Pol. J. Pharmacol. Pharm., 1981, 33, 141-147). Sydnocarb is also metabolized to D-amphetamine (D-AMPH) in humans and animals, but the sole of D-AMPH in the net in-vivo effects of sydnocarb is unclear. In vivo pharmacological profiles of sydnocarb and D-AMPH largely overlap, suggesting that either sydnocarb and D-AMPH are functionally indistinguishable or the metabolite D-AMPH contributes significantly to the effects produced by sydnocarb (Gainetdinov et al., supra; Witkin et al., J. Pharmacol. Exp. Ther., 1999, 288, 1298-1310); Anderzhanova et al., Ann. NY Acad. Sci. 2000, 914, 137-145; Flood et al., Psychopharmacology, 2010, 211, 325-336). However, there are some important differences between the two drugs. Unlike D-AMPH, neither significant toxic episodes nor abuse potential have been reported with sydnocarb in humans (Mashkovskii et al., Zh Nevropatol Psikhiatr Im S S Korsakova, 1971, 71, 1704-1709; Rudenko et al., supra). Compared with D-AMPH, the stimulating effects of sydnocarb develop more gradually, last longer, and are not accompanied by pronounced euphoria, motor excitation, or peripheral sympathomimetic effects such as tachycardia and hypertension (Rudenko et al., supra). In animals, sydnocarb produces a slower and more gradual increase in extracellular DA in the rat striatum and nucleus accumbens compared with D-AMPH (Gainetdinov et al., supra; Witkin et al., supra; Anderzhanova et al., supra). Relative to D-AMPH, equimolar doses of sydnocarb produce less hyperlocomotion and stereotype as well as smaller changes in the marker of neurotoxicity such as DA depletion, generation of reactive oxygen species, or increases in specific indices of lipid peroxidation (Gainetdinov et al., supra; Witkin et al., supra; Anderzhanova et al., supra; Afanas'ev et al., supra; Bashkatova et al., Ann. NY Acad. Sci., 2002, 965, 180-192). Furthermore, sydnocarb does not exhibit the rebound hypersomnolence seen with D-AMPH as a result of the dopamine release characteristics associated with D-AMPH (Gruner et al., supra). Several studies aimed at investigating the utility of DAT inhibitors in Parkinson's Disease have indicated very little or no utility towards this disease, especially as regards the potential utility of DAT inhibitors towards L-dopa-induced dyskinesias associated with Parkinson's Disease (Lökk, J., Neuropsych. Dis. Treat., 2010, 6, 93-97; Hauser et al., Mov. Disord., 2007, 22, 359-365; and Rascol et al., Arch Neurol., 2008, 65, 577-583).